Neurophysiology

Question 1

What are neuron’s?

Answer 1

The basic functional units of the nervous system. They take in information from other neurons (reception), integrate those signals (conduction), and pass signals to other neurons

Question 2

What are the two types of cells in the nervous system?

Answer 2

Neurons and Glial cells

Question 3

What are Glial cells?

Answer 3

They nourish, protect, and physically support neurons and are thought to be particularly critical in brain development.

Question 4

What is the oligodendrocyte?

Answer 4

They are a type of Glial cell that covers the axons of neurons with myelin, a substance critical to the effective functioning of the brain.

Question 5

What are the main parts of the neuron?

Answer 5

Dendrites

Axon hillock

Axon

Terminal buttons

Cell body (soma)

Question 6

What are dendrites?

Answer 6

Receive signals from other neurons which are integrated into the cell body. Based on the nature of those signals will transmit into the axon hillock.

Question 7

What is the axon hillock?

Answer 7

Where all cells are integrated. There is the decision point were a particular neuron is going to send a signal out via its axon, from the signals received from the dendrite.

Question 8

What is an axon?

Answer 8

The part of the neuron that stems from the dendrite to the terminal buttons.

Question 9

What is a terminal button?

Answer 9

The terminal inflated part of the axon, containing specialised apparatus necessary to release neurotransmitters.

Question 10

The terminal button of one neuron isn’t connected to another neurons dendrite, however there is a small gap. What is this gap? and what happens?

Answer 10

The small space is known as the synaptic cleft (or synaptic gap…or synapse)

When an action potential reaches the terminal buttons it causes the release of specialised chemicals (neurotransmitters) that travel across the synaptic cleft and are received by the dendrites of other neurons.

Note - the cell that sends the signal is called presynaptic and the one that receives the signal is called postsynaptic.

Question 11

What is the cell membrane made up of?

Answer 11

lipid bilayer - two layers of fatty molecules - where specialised proteins ‘float’.

Question 12

how do proteins move through the cells?

Answer 12

They form pores of channels that control movement of material into and out of the cell.

Question 13

What are Ions and ion channels?

Answer 13

Molecules that carry a positive or negative charge.

Ion channels allow molecules carrying a charge, to come in and out of the neuron.

Question 14

The cell membrane separates chemical solutions which interact via pores and channels, what are the molecules that move through them, what happens when they close?

Answer 14

Typically protein molecules, they move through a central passage.

They close when at rest, this prevents interchange of inside (intracellular) and outside (extracellular) materials.

Question 15

What is the action potential?

Answer 15

A brief reversal in the resting charge of the neuron. It is triggered by an exchange of ions across the neuron membrane.

Question 16

How is the action potential created?

Answer 16

Happens due to a particular exchange of sodium and potassium ions.

Action potential is triggered through the types of signals integrated from the dendrites at the axon hillock.

The trigger is around -55mV.

On the basis of the signals coming from the dendrites the resting membrane potential change from -70mV becomes more and more positive so are depolarised to around -55mV eliciting the threshold. Once that threshold is reached, an action potential will fire.

Question 17

What is the all-or-none principle?

Answer 17

If the threshold level is reached, an action potential of a fixed sized will always fire. For any given neuron, the size of the action potential is always the same.

It’s either full action potential or nothing at all.

Question 18

How is the speed of propagation of the action potential determined?

Answer 18

It is determined by the diameter of an axon (bigger = faster) and the presence or absence of a myelin sheath .

Question 19

What is the myelin sheath?

Answer 19

Electric insulator preventing current flow across membrane

Current can only flow across membrane at breaks in the myelin.

Question 20

What are the nodes of Ranvier?

Answer 20

Concentrated sodium channels in myelin breaks.

Action potentials can only be generated in these areas.

\__/\__/\__/\__/

Question 21

What happens when a neuron is at rest?

Answer 21

Typically, ion channels are closed. There is no movement of ions from inside the cell to inside the cell and vis versa.

Question 22

What is happening neuro-chemically when neurons are at rest?

Answer 22

The resting potential of the neuron is about -70mV

At rest there are more sodium ions (Na+) outside the cell than inside.

At rest there are more potassium ions (K+) inside the cell than outside.

(Going to bed Na+K+ed is when you are at rest)

Question 23

What happens at stage 1 of an action potential?

Answer 23

Neurotransmitters are stored in vesicles within the terminal button.

An action potential is fired in the pre-synaptic neuron there’s a change in polarity (or change in resting potential) that travels across the neuron will hit the terminal button.

Question 24

What happens at stage 2 in the action potential?

Answer 24

When the action potential is realised, the potential triggers the release of neurotransmitters within the terminal button into the synaptic cleft.

Question 25

What happens at stage 3 in the action potential?

Answer 25

neurotransmitters diffuse across the synaptic cleft. Some will attach to receptor molecules in postsynaptic membrane and activate them, thus enabling or inhibiting the postsynaptic neuron to generate the action potential.

Question 26

What are the two things that can happen at stage 3 of the action potential?

Answer 26

The binding of the chemical with the receptor on the post-synaptic neurons dendrite will make the resulting post-synaptic neuron either more positive or negative.

If a neurotransmitter binds with a receptor and depolarises the membrane, it is excitatory and increases the likelihood that the receiving neuron will fire an action potential.

If the neurotransmitter’s binding hyperpolarises the membrane, it is inhibitory and makes the receiving neuron less likely to fire an action potential.

Question 27

What does Acetylcholine do (ACh)?

Answer 27

Activates motor neurons controlling skeletal muscles. Contributes to the regulation of attention, arousal, and memory.

Question 28

Dopamine (DA)

Answer 28

Contributes to control of voluntary movement. Important in reward, motivation, and pleasurable emotions.

Question 29

Serotonin (5-HT)

Answer 29

Important in emotional states, impulsiveness, and dreaming.

Question 30

GABA

Answer 30

Serves as a widely distributed inhibitory neurotransmitter.

Gaba always has an inhibitory action.

Question 31

Endorphins

Answer 31

Resemble opiate drugs in structure and effects. Contribute to pain relief and some pleasurable emotions.

Question 32

Neurotransmitters are crucial as they bind with a receptors, what are the two things they critically do?

Answer 32

When they depolarise the membrane they are excitatory and increase the likelihood that the receiving neuron will fire an action potential.

Sometimes we need to stop our brains from processing things, this happens through inhibition, this is how our brain can function so well.

Question 33

How do drugs work on neurotransmitters to treat depressio?

Answer 33

Selective serotonin reuptake inhibitors, this makes more serotonin available in synapses making serotonin play a role in emotional states.

Question 34

What are the three effects in terminating synaptic transmission?

Answer 34

Reuptake - the whole neurotransmitter molecule is taken back into the axon terminal that released it.

Diffusion - the neurotransmitter drifts away, out of the synaptic cleft where it can no longer act on a receptor.

Deactivation - A specific enzyme changes the structure of the neurotransmitter so it is not recognised by the receptor.

Question 35

What are agonistic and antagonistic drug effects?

Answer 35

Agonistic
Enhances the effectiveness of a neurotransmitter.

Antagonistic
Anything that makes a neuro transmitter less effective